A planar Fourier capture array (PFCA) an image sensor that does not require a lens, mirror, focal length, or moving parts. As a consequence, cameras that employ PFCAs to acquire image data can be made extraordinarily small and inexpensive.
PFCAs include angle-sensitive pixels that are sensitive to light that is sinusoidal in incident angle along the optically-sensitive axis, which can be interpreted as a measure of one component of the 2D Fourier transform of a far-away scene. Each pixel has physical characteristics that make is sensitive to a distinct component of the 2D Fourier transform of the far-away scene. Taken together, these components relate full Fourier information representative of the scene. Some applications may use the Fourier components directly, or images of the scene can be computationally reconstructed.
PFCAs exploit a near-field diffraction effect called named for Henry Fox Talbot (the “Talbot effect”). Briefly, a plane wave incident upon a periodic diffraction grating produces a repeating image of the grating at regular distances away from the grating plane. PFCAs image one of the repeating “Talbot images.” Unfortunately, it can be very difficult to manufacture devices with interlayer depths precise enough to ensure that image sensors positioned beneath a diffraction grating fall precisely at one of the regular distances that accurately reproduce a Talbot image. In standard CMOS processes, for example, interlayer thicknesses can vary by 20%. To make matters more difficult, Talbot spacing is a strong function of wavelength, making it exceedingly difficult to produce sharp Talbot images over a wavelength band of interest (e.g., the visible light spectrum).